The present invention relates to a radiation curable adhesive composition comprising at least one vinyl modified block copolymer having polyvinyl aromatic (styrenic) endblocks and polydiene midblocks having vinyl functionality. The adhesive composition exhibits at least one of a variety of improved adhesive performance characteristics depending on the type and amount of the ingredients selected.
xe2x80x9cUV Crosslinkable Styrenic Block Copolymers . . . A Door to High Temperature Heat Resistant Hot Melt Adhesive Applicationsxe2x80x9d by Martine Dupont, the Journal of the Adhesive and Sealent Council, Inc., 1997 Spring Convention, Pittsburgh, Pa. Mar. 23-26, 1997, pp 229-240, discloses compositions containing 25 to 35 wt-% of a block copolymer KX-222C, a solid hydrogenated tackifying resin Regalite R91 or MBG 264, a hydrogenated liquid resin Regalrez 1018, a photoinitiator Irgacure 651 and an antioxidant Irganox 1010. The composition exhibits the lowest viscosity of 10 Pa.s at 160xc2x0 C.
U.S. Pat. No. 5,804,663 discloses radiation sensitive vinyl aromatic block copolymers and radiation curable adhesives, sealants, and coatings containing such block copolymers. The radiation sensitive block copolymers contain at least one block derived from vinyl aromatic monomer and at least one block derived from butadiene. The adhesive exhibits the lowest viscosity of 6.7 Pa.s at 160xc2x0 C.
In one embodiment, the invention is directed to a radiation curable adhesive composition that is amenable to being applied at a low application temperature, i.e., an application temperature no greater than about 150xc2x0 C. Preferably, the application temperature is no greater than about 140xc2x0 C. and more preferably, no greater than about 130xc2x0 C. The adhesive composition comprises from about 10 wt % to about 40 wt %, of at least one vinyl modified block copolymer having polyvinyl aromatic (styrenic) endblocks and vinyl functionalized polydiene midblocks, and from about 20 wt % to about 90 wt % of at least one tackifier. The vinyl functionality of the polydiene block presents reactively favorable sites and is at a sufficient concentration such that the block copolymer crosslinks substantially through the vinyl functionality upon exposure to radiant energy. The adhesive composition may further comprise at least one plasticizer. Preferably, from about 30 wt % to about 90 wt % of the ingredients comprised of the composition are liquids at ambient temperature. Preferably, the liquid ingredients comprise a mixture of at least one polydiene block compatible tackifier and at least one polyvinyl aromatic block compatible plasticizer. The adhesive composition may further comprise up to about 40 wt %, preferably from about 5 wt % to about 40 wt %, more preferably from about 5 wt % to about 20 wt %, of at least one second polymer such that the total polymer content in the composition is at least about 15 wt %. The second polymer may also be radiation sensitive, i.e., able to substantially crosslink upon exposure to radiant energy, or may not be radiation sensitive. The adhesive composition has a Brookfield viscosity of less than about 10,000 cps and preferably, less than about 6,000 cps at a temperature of about 160xc2x0 C.
In another embodiment, the invention is directed to a radiation curable adhesive composition comprising from about 10 wt % to about 40 wt % at least one vinyl modified block copolymer having at least two blocks, wherein the first block is a polyvinyl aromatic block and the second block is a polydiene block having vinyl functionality, from about 10 wt % to about 80 wt % of at least one tackifier that is compatible with the polydiene block; and from about 10 wt % to about 40 wt % of at least one plasticizer. The plasticizer is preferably a polyvinyl aromatic block compatible plasticizer having softening point of no greater than 100xc2x0 C.; a high molecular weight polydiene block compatible plasticizer having a weight average molecular weight of no less than about 20,000 g/mol, preferably, up to about 100,000 g/mol, such as polyisoprene, or mixtures thereof.
In yet another embodiment, the invention is directed to a radiation curable adhesive composition comprising from about 10 wt % to about 40 wt % of at least one vinyl modified block copolymer having at least two blocks, wherein the first block is a polyvinyl aromatic block and the second block is a polydiene block having vinyl functionality; from about 5 wt % to about 40 wt % of at least one second polymer selected from the group consisting of styrenic block copolymers, ethylene/xcex1-olefin interpolymers, amorphous polyalphaolefins, interpolymers of ethylene, and mixtures thereof, and from about 10 wt % to about 90 wt % of at least one tackifier.
In yet another embodiment, the invention is directed to a radiation curable adhesive composition comprising from about 10 wt % to about 50 wt % of at least one vinyl modified block copolymer having at least two blocks, wherein the first block is a polyvinyl aromatic block and the second block is a polydiene block having vinyl functionality; from about 20 wt % to about 55 wt % of at least one tackifier; from about 10 wt % to about 40 wt % of at least one wax; and from about 0 wt % to about 35 wt % of at least one plasticizer. The adhesive is not substantially tacky at a temperature of lower than the cloud point of the wax. The adhesive exhibits high shear resistance at high temperature, therefore, is appropriate for stretchable labels.
In yet another embodiment, the invention is directed to a double-faced tape formed from a single radiation curable adhesive composition, said double-faced tape having a first surface and a second opposing surface, said first surface exhibiting a first 180xc2x0 peel value and said second surface exhibiting a second 180xc2x0 peel value that is greater than said first peel value, upon radiation curing; and to a method of producing the double-faced tape comprising applying an adhesive composition onto a release-coated surface to form an adhesive film layer and curing the adhesive film such that the adhesive film exhibits different adhesive properties on one surface than the opposing surface.
In yet another embodiment, the invention is directed to a plastic wrap comprising a film and an adhesive composition disposed on one surface of said film, said adhesive composition exhibits a storage modulus (Gxe2x80x2) of less than about 1xc3x97105 dynes/cm2 at about 25xc2x0 C. Preferably, the storage modulus is within the pressure sensitive adhesive region as defined by the Dahlquist criteria through a temperature range of from about 0xc2x0 C. to about 120xc2x0 C.
In yet another embodiment, the invention is directed to a hook or loop substrate bonded with a radiation curable adhesive composition of the invention.
In yet another embodiment, the invention is directed to a disposable article having at least one substrate bonded with a radiation cured adhesive composition of the invention, wherein said adhesive composition is in contact with an oil-based skin care ingredient.
The adhesive compositions of the invention are amenable to a variety of end-uses, particularly for pressure sensitive adhesives for high performance tapes and labels such as freezer-grade tapes and labels, and automotive adhesives as well as for various adhesive applications wherein adhesion to wet surface is desired, such as medical products that employ an adhesive.
The radiation curable adhesive compositions can be formulated to exhibit higher peel values, higher heat resistance, improved cold temperature properties particularly at temperatures below 0xc2x0 C., improved adhesion to wet surfaces and/or improved solvent and plasticizer resistance.